US20070093844A1 - Calcar planers for minimally invasive surgery - Google Patents

Abstract

Calcar planers for minimally invasive surgery. The calcar planers each generally include a shaft including a power equipment interface for coupling to a power source for imparting rotary motion to the calcar planer. The shaft is connected to a cutting head via a coupling portion. The coupling portion may include a flexible coupling or a flexible segmented portion structure. Alternatively, the coupling portion may include a gear arrangement. In another embodiment, the coupling portion may include a constant velocity universal joint structure.

Description

BACKGROUND
• 1. Field of the Invention
• The present invention relates to calcar planers, and, more particularly, to calcar planers for minimally invasive surgery.
• 2. Description of the Prior Art
• During a total hip arthroplasty (THA), a surgeon typically creates an incision proximate the hip of a patient and subsequently reams a cavity in the intramedullary canal of the femur of the patient. The surgeon may then temporarily implant a rasp into the reamed cavity. The rasp includes a broach pin protruding from a proximal end of the rasp. The protruding broach pin is used as a bearing trunnion or guide pin for placement of a calcar planer. In operation, the calcar planer is inserted into the patient via the incision and mates with the broach pin of the rasp via a socket formed in the cutting head of the calcar planer. Upon mating the broach pin and the socket, the calcar planer is rotated to perform a planing of the calcar surface on the proximal femur. Once the calcar surface is sufficiently flat for the desired application, the surgeon removes the calcar planer from the patient.
• Conventional calcar planers include a straight, rigid shaft directly connecting the cutting head to a rotation-imparting power source. In some circumstances involving minimally invasive surgery, a direct access to the broach pin via the incision may not be available due to the reduced size and/or placement of the incision. The rigid construction of a conventional calcar planer could potentially require a surgeon to enlarge the entry incision to prevent the shaft of the calcar planer from impinging on the edge of the incision.
SUMMARY
• The present invention provides calcar planers for minimally invasive surgery. A calcar planer in accordance with the present invention generally includes a shaft having a longitudinal axis including a power equipment interface for coupling to a power source for imparting rotary motion to the calcar planer. The shaft is connected via a coupling portion to a cutting head having a longitudinal axis. The coupling portion may include a flexible coupling or a flexible segmented structure. Alternatively, the coupling portion may include a gear arrangement. In another embodiment, the coupling portion may include a constant velocity universal joint (U-joint) structure. In each of the foregoing embodiments, the cutting head longitudinal axis of the calcar planer of the present invention is either selectively or fixedly non-coaxial with the shaft longitudinal axis.
• When the cutting head longitudinal axis is non-coaxial with the shaft longitudinal axis, torque is advantageously transmitted from the shaft to the cutting head via the coupling portion. The coupling portion advantageously permits transmission of rotational torque even when the shaft is not aligned with the cutting head. When misaligned, the power source transmits torque to the shaft which, in turn, transmits rotational motion to the coupling portion. The coupling portion transmits the rotational motion around the angle formed by the shaft and the cutting head to the cutting head. The coupling portion advantageously permits a surgeon to angularly move the shaft about the cutting head longitudinal axis while still simultaneously transmitting torque from the shaft to the cutting head.
• In one form thereof, the present invention provides a calcar planer for use in planing a calcar surface of a bone including a shaft including a first longitudinal axis; a cutting head including a second longitudinal axis; and a torque transmitting coupler connecting the shaft and the cutting head, the coupler transferring torque between the shaft and the cutting head when the first and second axes are coaxially aligned and when the first and second axes are not coaxially aligned.
• In another form thereof, the present invention provides a calcar planer for use in planning a calcar surface of a bone including a shaft including a first longitudinal axis; a cutting head including a second longitudinal axis; and torque transmission coupler means connecting the shaft and the cutting head for transferring torque between the shaft and the cutting head while concurrently allowing axial misalignment between the first and second axes.
• In yet another form thereof, the present invention provides a calcar planer for use in planing a calcar surface of a bone including a shaft including a first longitudinal axis; a cutting head including a second longitudinal axis; a torque transmitting coupler connecting the shaft and the cutting head, the coupler transferring torque between the shaft and the cutting head when the first and second axes are coaxially aligned and when the first and second axes are not coaxially aligned; a flexible sheath disposed around the torque transmitting coupler; and a handle, the handle connected to the calcar planer proximate the cutting head.
BRIEF DESCRIPTION OF THE DRAWINGS
• The above mentioned and other features and objects of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
• FIG. 1A is a perspective view of an exemplary calcar planer of the present invention;
• FIG. 1B is another perspective view of the calcar planer ofFIG. 1A;
• FIG. 1C is a perspective view of the calcar planer ofFIG. 1A, additionally showing a handle coupled to the planer;
• FIG. 1D is a fragmentary perspective view of an alternative embodiment of a calcar planer of the present invention;
• FIG. 2A is a perspective view of another alternative embodiment calcar planer of the present invention;
• FIG. 2B is an enlarged view of a portion of yet still another embodiment calcar planer, further illustrating the gear set in a cutaway portion of the calcar planer;
• FIG. 2C is a perspective view of the calcar planer ofFIG. 2A, additionally showing a handle coupled to the planer;
• FIG. 3A is a perspective view of another alternative embodiment calcar planer of the present invention;
• FIG. 3B is a close-up view of a portion of the calcar planer ofFIG. 3A;
• FIG. 3C is a perspective view of the calcar planer ofFIG. 3A, additionally showing a handle coupled to the planer;
• FIG. 3D is an enlarged view of a portion of the calcar planer ofFIG. 3C; and
• FIG. 4 is a perspective view of the calcar planer ofFIG. 1A shown in operational relationship with a calcar surface of a femur.
• Corresponding reference characters indicate corresponding parts throughout the several views. Although the drawings represent embodiments of the present invention, the drawings are not necessarily to scale and certain features may be exaggerated in order to better illustrate and explain the present invention. The exemplifications set out herein illustrate embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
DETAILED DESCRIPTION
• The embodiments disclosed below are not intended to be exhaustive or limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may utilize their teachings.
• In general, the present invention provides calcar planers for minimally invasive surgery. As illustrated inFIGS. 1A-1D,2A-2C, and3A-3D,calcar planers20,20′, and20″, respectively, each generally includeshaft22 includingpower equipment interface28 for coupling to a power source (not shown) for imparting rotary motion tocalcar planers20,20′, and20″.Shaft22 is connected to cuttinghead24 via a coupling portion. The coupling portion may include flexible coupling30 (FIGS. 1A-1C) or flexiblesegmented portion30′(FIG. 1D). Alternatively, the coupling portion may include gear arrangement40 (FIGS. 2A-2C). In another embodiment, the coupling portion may include constant velocity U-joint50 (FIGS. 3A-3D) or U-joint50′(not shown).
• When cutting headlongitudinal axis27 is non-coaxial with shaftlongitudinal axis21, torque is advantageously transmitted fromshaft22 to cuttinghead24 via the coupling portion. The coupling portion advantageously permits transmission of rotational torque even whenshaft22 is not aligned with cuttinghead24. When misaligned, the power source transmits torque toshaft22 which, in turn, transmits rotational motion to the coupling portion. The coupling portion transmits the rotational motion around the angle formed byshaft22 and cuttinghead24 to cuttinghead24. The coupling portion advantageously permits a surgeon toangularly move shaft22 about cutting headlongitudinal axis27 while still simultaneously transmitting torque fromshaft22 to cuttinghead24.
• Flexible Coupling Embodiment
• Referring now toFIG. 1A,calcar planer20 includesshaft22 and cuttinghead24 coupled together via coupling portion orflexible coupling30.Shaft22 includespower equipment interface28 configured to permitshaft22 to be coupled to a power source (not shown), such as a rotary drill, for imparting rotary motion tocalcar planer20 during use.Shaft22 also includeslongitudinal axis21 extending along a length thereof. As shown inFIG. 1B, cuttinghead24 includes cuttingsurface23 having a plurality of cuttinghead teeth25 and cuttinghead socket26. Cuttinghead teeth25 are arranged on cuttingsurface23 along chord lines of the circle defined by cuttingsurface23. Each chord line along which each cuttinghead tooth25 is arranged is perpendicular to an adjacentcutting head tooth25. Cuttinghead24 also includeslongitudinal axis27 which extends perpendicular to the planar surface which includes cuttingsurface23.
• In one embodiment,flexible coupling30 may be formed of a material such that the material resumes its original shape when a deforming force is removed and such that the material provides torsional rigidity tocalcar planer20. The material constitutingflexible coupling30 may be such as to permitlongitudinal axis27 of cuttinghead24 to be selectively moved from coaxial alignment into non-coaxial alignment withlongitudinal axis21 ofshaft22 at the discretion of the surgeon, advantageously permittingshaft22 to be angularly moved aboutlongitudinal axis27 while still simultaneously transmitting torque fromshaft22 to cuttinghead24.Flexible coupling30 may be formed of any material which provides a spring-type force which keepslongitudinal axis21 ofshaft22 in straight alignment withlongitudinal axis27 of cuttinghead24 without any bending force applied thereto, and facilitates the return to a straight alignment betweenlongitudinal axes21 and27 after a bending force has been removed. Such material may include a vulcanized rubber material, an elastomer, e.g., rubber, a polymer material, polytetrafluoroethylene (PTFE), or polyethylene. Torque may be transmitted viaflexible coupling30 without a supporting structure therein ifflexible coupling30 is formed of a suitable material, e.g., vulcanized rubber. Alternatively,flexible coupling30 may be formed as a cable with sufficient flexibility and constructed of a shape-memory metal alloy, e.g., nitinol, with a sheath formed of any of the above-listed materials which surrounds the flexible cable. Such an exterior sheath prevents any blood, tissue, or other bodily waste from interfering with the workings of the internal mechanism.
• In one embodiment, as shown inFIG. 1C,calcar planer20 may include handle29.Handle29 may be attached on any portion ofcalcar planer20, but is shown attached betweenflexible coupling30 and cuttinghead24 inFIG. 1C.Handle29 facilitates the surgeon's ability to control cuttinghead24 during operation and to accurately place cuttinghead socket26 onto broach pin65 (FIG. 4), as discussed below.Handle29 includes an internal bushing (not shown) wherebycalcar planer20 may rotate in the bushing and handle29 does not rotate withcalcar planer20.Handle29 advantageously provides enhanced control of the torque reaction resulting from rotation ofcalcar planer20.
• In an alternative embodiment shown inFIG. 1D,calcar planer20 may include flexiblesegmented portion30′which couplesshaft22 and cuttinghead24. Flexiblesegmented portion30′ may take the form of a flexible accordion-type structure or a bellows-type structure and may be constructed with a pleated, expandable material which is able to be expanded and contracted as well as manipulated to form a flexible, curved shape. As similarly described above with respect toflexible coupling30, flexiblesegmented portion30′ advantageously permits a surgeon to modify the orientation ofshaft22 with respect to cuttinghead24 while transmitting rotational torque fromshaft22 to cuttinghead24. Such modification may makelongitudinal axis27 of cuttinghead24 non-coaxial withlongitudinal axis21 ofshaft22. Flexiblesegmented portion30′ may be constructed of a plastic or polymer material, a metal alloy, or a woven fabric or textile.
• Gear Arrangement Embodiment
• Referring now toFIG. 2A,calcar planer20′ includesshaft22 and cuttinghead24 coupled together via a coupling portion, shown as agear arrangement40.Gear arrangement40 may includefirst gear41 attached throughgear arrangement housing43 toshaft22 andsecond gear42 attached throughgear arrangement housing43 to cuttinghead24. The connections offirst gear41 andsecond gear42 toshaft22 and cuttinghead24, respectively, throughgear arrangement housing43 may include internal bushings to facilitate transmittal of rotary motion tofirst gear41 fromshaft22 and cuttinghead24 fromsecond gear42.First gear41 andsecond gear42 are in meshing engagement to transmit rotational motion fromshaft22 to cuttinghead24. Upon rotation ofshaft22, the teeth offirst gear41 rotate and matingly engage the teeth ofsecond gear42. Upon engagement with the rotating teeth offirst gear41, the teeth ofsecond gear42 rotate and cause cuttinghead24 to rotate.
• Gear arrangement housing43 housesfirst gear41 andsecond gear42 and may be formed out of any suitable biocompatible material. In one embodiment as shown inFIG. 2B,gear arrangement housing43 completely encapsulatesfirst gear41 andsecond gear42 in a sealed housing.FIG. 2B shows a cutaway portion revealingfirst gear41 andsecond gear42. The sealed housing prevents any wound debris from enteringgear arrangement housing43 which may obstructfirst gear41 andsecond gear42. In the sealed housing arrangement, the connections offirst gear41 andsecond gear42 toshaft22 and cuttinghead24, respectively, throughgear arrangement housing43 may also be sealed with, for example, gaskets.
• Referring again toFIG. 2A, in one embodiment,gear arrangement40 disposeslongitudinal axis21 ofshaft22 perpendicular tolongitudinal axis27 of cuttinghead24. Advantageously, such a configuration allowsfirst gear41 andsecond gear42 to be cost-effectively cut at a 45° bevel to provide a fixed, 90° power transmission. Alternatively,first gear41 andsecond gear42 may be cut such as to provide any degree of power transmission desired by an end user ofcalcar planer20′.Gears41 and42 are cut at approximately ½ of the desired angle betweenlongitudinal axis21 ofshaft22 andlongitudinal axis27 of cuttinghead24, for example, gears41 and42 may be cut at a 67.5° angle to allowshaft22 to be at a 135° angle with respect to cuttinghead24.
• In one embodiment, as shown inFIG. 2C,gear arrangement housing43 includeshandle29 extending therefrom.Handle29 may be integrally formed withhousing43 or handle29 may be attached with fasteners (not shown) ifhandle29 is constructed as a separate piece. Alternatively, handle29 may be attached toshaft22 immediately proximal tohousing43 similar to the attachment ofhandle29 tocalcar planer20, as described above, or handle29 may be attached to cuttinghead24 in a similar manner.
• Constant Velocity U-Joint Embodiment
• A universal joint (U-joint) is a flexible double-pivoted joint that allows driving power to be carried through two shafts that are at an angle to each other. A U-joint consists of two Y-shaped yokes and a cross-shaped member called the spider. Ordinary U-joints cause a change in speed between a driving shaft and a driven shaft whenever the U-joint operates at an angle. As the operating angle of the U-joint increases, the speed of the driven shaft varies more and more during each revolution. The greater the operating angle, the greater the variation in speed of the driven shaft and the greater the vibration produced.
• The driven shaft still turns at the same number of revolutions per minute as the driving shaft, but because of the geometry of a U-joint, the speed of the driven shaft alternately increases (accelerates) and decreases (decelerates) four times every revolution, thereby causing vibration of the driven shaft. The speed changes are not great when the angle is less than a few degrees, but as the operating angle of the U-joint increases, so do the cyclic vibrations of the driven shaft as well as the back and forth motion in the U-joint itself.
• To combat the negative effects of an ordinary U-joint, a second U-joint can be used which is phased in line with respect to the first U-joint to form a constant velocity U-joint. The second U-joint cancels out the changes in output velocity caused by the first U-joint, but only so long as both U-joints operate at identical angles. Thus, no matter what the angle between the first U-joint and the second U-joint, there are no changes in speed of the driven shaft.
• Referring now toFIG. 3A,calcar planer20″ includesshaft22 and cuttinghead24 coupled together via coupling portion or constant velocity universal joint (U-joint)50. As shown inFIG. 3B,shaft22 may include U-portion oryoke51 located at a distal end thereof and cuttinghead24 may include U-portion oryoke53 located opposite cuttingsurface23 on a proximal side of cuttinghead24.U-portion51 and U-portion53 are coupled together viaU-joint coupler55 and secured thereto viaspiders52 and54, respectively. In an alternative embodiment, the coupling portion comprises U-joint50′ (not shown) whereinU-joint coupler55 is absent andU-portion51 is directly connected to U-portion53 via a spider.
• Constant velocity U-joint50, as shown inFIGS. 3A and 3B, transmits rotational motion fromshaft22 to cuttinghead24 at a constant velocity. Upon rotation ofshaft22,U-portion51 transmits elliptical rotation toU-joint coupler55. Upon rotation across the major axes of the ellipse, the rotational velocity is very high. In contrast, upon rotation across the minor axes of the ellipse, the rotational velocity is very low. To compensate and achieve constant velocity rotation, the interaction ofU-joint coupler55 withU-portion53 of cuttinghead24forces cutting head24 to rotate at a constant velocity because during the rotation across the major axes of the ellipse byU-portion51,U-portion53 is also rotating across the major axes of its ellipse, thereby nullifying any speed change provided by rotation ofU-portion51. Similarly, during the rotation across the minor axes of the ellipse byU-portion51,U-portion53 is also rotating across the minor axes of its ellipse, thereby nullifying any speed change caused by rotation ofU-portion51. The interaction and configuration of constant velocity U-joint50 transmits a constant velocity rotational motion fromshaft22 to cuttinghead24.
• In an alternative embodiment, as shown inFIGS. 3C and 3D,calcar planer20″ may include handle29 attached between constant velocity U-joint50 and cuttinghead24 similar to handle29, as described above with respect tocalcar planer20 inFIG. 1C.
• Flexible Coupling Combined with U-Joint Embodiment
• In another embodiment,flexible coupling30, as shown inFIGS. 1A-1C, or flexiblesegmented portion30′, as shown inFIG. 1D, may be combined with constant velocity U-joint50, as shown inFIGS. 3A-3D. In this embodiment, constant velocity U-joint50 may be encompassed withinflexible coupling30 or flexiblesegmented portion30′, thereby providing a shielding effect to constant velocity U-joint50 from any wound debris while simultaneously enhancing the ability to makelongitudinal axis21 ofshaft22 selectively non-coaxial withlongitudinal axis27 of cuttinghead24.Flexible coupling30 or flexiblesegmented portion30′ may provide a flexible sheath, i.e., a protective and enveloping covering or structure, which may be positioned around constant velocity U-joint50 or U-joint50′ (not shown).
• Method of Operation
• Referring now toFIG. 4, during a total hip arthroplasty (THA), a surgeon creates an incision (not shown) proximate the hip of a patient (not shown) and subsequently reams a cavity inintramedullary canal62 offemur60 of the patient. The surgeon may then temporarily implantrasp64 into the reamed cavity.Rasp64 includesbroach pin65 protruding from a proximal end ofrasp64. The protrudingbroach pin65 is used as a bearing trunnion or guide pin for placement ofcalcar planer20. In operation,calcar planer20 is inserted into the patient via the incision and mates withbroach pin65 ofrasp64 via cuttinghead socket26 formed in cuttinghead24 ofcalcar planer20. Uponmating broach pin65 and cuttinghead socket26,calcar planer20 is rotated to perform a planing ofcalcar surface61 on the proximal end offemur60. Once calcar surface61 is sufficiently flat for the desired application, the surgeon removescalcar planer20 from the patient.
• During insertion ofcalcar planer20,flexible coupling30 permits efficient access to broachpin65 with a minimally invasive incision. Due to the minimally invasive incision, the surgeon has very little space to manipulatecalcar planer20 to matebroach pin65 with cuttinghead socket26.Flexible coupling30 permits a surgeon to control the orientation oflongitudinal axis27 of cuttinghead24 andlongitudinal axis21 ofshaft22 andplace axis27 andaxis21 in a non-coaxial arrangement, as shown inFIG. 4. Such selective flexibility permits a surgeon to maintain the original, minimal size of the minimally invasive incision without having to enlarge the incision to prevent impingement ofshaft22 on the edge of the incision while guidingcutting head socket26 into mating engagement withbroach pin65. During rotation,flexible coupling30 permits the surgeon to maintaincalcar planer20 in an arrangement whereinaxis27 andaxis21 are in a non-coaxial arrangement which again permits the surgeon to maintain the original size of the incision without being required to enlarge the incision to prevent impingement ofrotating shaft22 on the edge of the incision. Such arrangement is facilitated through the use of handle29 (FIG. 1C) which not only helps maintain the non-coaxial arrangement but also helps the surgeon compensate for the torque reaction ofcalcar planer20 upon rotation.
• While this invention has been described as having exemplary designs, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.

Claims (18)

1. A calcar planer for use in planing a calcar surface of a bone, comprising:

a shaft including a first longitudinal axis;

a cutting head including a second longitudinal axis; and

a torque transmitting coupler connecting said shaft and said cutting head, said coupler transferring torque between said shaft and said cutting head when said first and second axes are coaxially aligned and when said first and second axes are not coaxially aligned.

2. The calcar planer ofclaim 1, wherein said coupler comprises a flexible coupler which enables said first and second axes to be selectively not coaxially aligned.

3. The calcar planer ofclaim 1, wherein said coupler comprises a constant velocity universal joint, said constant velocity universal joint transmitting constant rotational velocity from said shaft to said cutting head when said first and second axes are coaxially aligned and when said first and second axes are not coaxially aligned.

4. The calcar planer ofclaim 3, wherein said coupler further comprises a flexible sheath disposed around said constant velocity universal joint.

5. The calcar planer ofclaim 1, wherein said coupler comprises a gear set including a first gear and a second gear, said first gear in meshing engagement with said second gear, said first gear connected to said shaft, and said second gear connected to said cutting head.

6. The calcar planer ofclaim 5, wherein said gear set is housed within a substantially enclosed housing portion.

7. The calcar planer ofclaim 1, further comprising a handle, said handle connected to the calcar planer proximate said coupler.

8. A calcar planer for use in planning a calcar surface of a bone, comprising:

a shaft including a first longitudinal axis;

a cutting head including a second longitudinal axis; and

torque transmission coupler means connecting said shaft and said cutting head for transferring torque between said shaft and said cutting head while concurrently allowing axial misalignment between said first and second axes.

9. The calcar planer ofclaim 8, wherein said coupler means comprises a flexible coupler which enables said first and second axes to be selectively not coaxially aligned while still transferring torque between said shaft and said cutting head.

10. The calcar planer ofclaim 8, wherein said coupler means comprises a constant velocity universal joint, said constant velocity universal joint transmitting constant rotational velocity from said shaft to said cutting head while said first and second axes are not coaxially aligned.

11. The calcar planer ofclaim 10, wherein said coupler means further comprises a flexible sheath disposed around said constant velocity universal joint.

12. The calcar planer ofclaim 8, wherein said coupler means comprises a gear set including a first gear and a second gear, said first gear in meshing engagement with said second gear, said first gear connected to said shaft, and said second gear connected to said cutting head, said gear set transmitting torque from said shaft to said cutting head through meshing engagement of said first gear with said second gear.

13. The calcar planer ofclaim 12, wherein said gear set is housed within a substantially enclosed housing portion.

14. The calcar planer ofclaim 8, further comprising a handle, said handle connected to the calcar planer proximate said coupler means.

15. A calcar planer for use in planing a calcar surface of a bone, comprising:

a shaft including a first longitudinal axis;

a cutting head including a second longitudinal axis;

a torque transmitting coupler connecting said shaft and said cutting head, said coupler transferring torque between said shaft and said cutting head when said first and second axes are coaxially aligned and when said first and second axes are not coaxially aligned;

a flexible sheath disposed around said torque transmitting coupler; and

a handle, said handle connected to the calcar planer proximate said coupler.

16. The calcar planer ofclaim 15, wherein said coupler comprises a constant velocity universal joint, said constant velocity universal joint transmitting constant rotational velocity from said shaft to said cutting head when said first and second axes are coaxially aligned and when said first and second axes are not coaxially aligned.

17. The calcar planer ofclaim 15, wherein said coupler comprises a flexible cable.

18. The calcar planer ofclaim 15, wherein said coupler comprises a gear set including a first gear and a second gear, said first gear in meshing engagement with said second gear, said first gear connected to said shaft, and said second gear connected to said cutting head, said gear set transmitting torque from said shaft to said cutting head through meshing engagement of said first gear with said second gear.

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